Vehicles with an electrified powertrain include an internal combustion engine that is used as a primary driver of the vehicle, and incorporate at least one electric motor-generator to either generate electrical power from torque provided from the engine when the engine is producing excess torque, or provide additional torque to the engine to assist the engine when the engine requires additional torque production.
Vehicles with an electrified powertrain tend to be either a single voltage system, or a dual voltage system. Vehicles with an electrified powertrain using the single voltage system generally rely on a single high-power energy storage device (generally at a nominal 12 volts) to provide electrical energy for accessory loads when the engine is off, engine cranking for starting, engine torque addition, etc. The single high-power energy storage device also absorbs electrical energy from the motor-generator when the vehicle is braking or when the motor-generator is providing more electrical power than the accessory loads require. Vehicles with an electrified powertrain using the dual voltage system generally rely on two different energy storage devices. The primary or cranking energy storage device is nominally a 12 volt device, and is used to provide energy for loads during key-off situations. The cranking energy storage device is also used to provide energy during starting events. The second energy storage device is typically of a higher voltage, and is generally charged by the motor-generator at the higher voltage. A dc-dc converter is required to transfer energy from the higher voltage energy storage device and/or the motor generator to the lower voltage (e.g., 12 volt) cranking energy storage device and/or to the accessory loads.